1. Field of the Invention
This invention relates to an endoscope system including a light source apparatus for supplying illumination light to an endoscope in which light adjustment is controlled according to an upgraded sequence.
2. Description of the Related Art
In recent years, an endoscope having an elongated insertion unit has prevailed in the field of medicine. The insertion unit is inserted into a body cavity and thus enabling diagnosis of a lesion or the like in the body cavity without the necessity of incising it, or if necessary, enabling insertion of a treatment instrument into the body cavity for the purpose of cure.
Illumination light emanating from a light source apparatus or the like is propagated to the distal part of the insertion unit over a light guide or the like. The illumination light is irradiated to an object region such as a lesion via an illumination optical system through the distal part. An image of the object region such as a lesion is formed by an objective lens located in the distal part of the insertion unit. An optical image is transmitted to an eyepiece unit by means of an optical transmission means. An eyepiece optical system then enables the optical image to be viewed.
The optical transmission means varies depending on the usage or purpose of use. For example, a fiber bundle is used for a flexible endoscope, while a relay lens is used for a rigid endoscope.
In an electronic endoscope, which includes a solid-state imaging device, (for example, a CCD) in the distal part of an insertion unit, an optical image is formed on the image formation surface of the CCD via an objective lens. The CCD photoelectrically converts the optical image so as to provide image information in the form of an electrical signal. The image information is subjected to various kinds of image processing, and thus a desired image of an object region is displayed on a monitor or the like.
In recent years, image processing techniques have greatly improved. With the improved techniques, various kinds of image processing can be performed on the image information. For example, an endoscopic image can be enlarged, an image of a lesion or the like can be processed, or relevant images can be compared with each other. This leads to easy and accurate diagnosis. This kinds of processing of endoscopic images can be achieved even in an endoscope having a conventional optical transmission means. That is to say, when a camera head having a CCD or the like located in an eyepiece unit is freely detachably attached to the endoscope having a conventional optical transmission means, an optical image can be converted photoelectrically and processed in the form of image information.
An image produced by the foregoing electronic endoscope suffers from problems since a distance from the distal part of the insertion unit to an object is variable. If an object such as lumina or a quite irregular object must be imaged, irregular illumination occurs to being about a phenomenon that halation happens to a near object in the same picture but a far object becomes too dark to be visible.
For coping with the problem of irregular illumination, the prior art has proposed a technique of adjusting the light emanating from a light source apparatus by controlling a diaphragm drive circuit, which is included in the light source apparatus and supplies illumination light to an endoscope. The light control is accomplished according to a light adjustment signal produced from an image signal sent from a CCD. This prior art technique alleviates the irregular illumination and is disclosed in, for example, Japanese Unexamined Patent Publication No. 62-155689.
However, when an endoscope is removed from a human body, the amount of source light emanating from a light source apparatus should preferably be decreased. When the endoscope is removed from a human body, since an object to be illuminated by the light source apparatus disappears, the level of a video signal is lowered. A light adjustment unit described in the Japanese Unexamined Patent Publication No. 62-155689 controls the diaphragm drive circuit in the light source apparatus according to the light adjustment signal produced from the image signal. Upon removal of the endoscope from the body, since the level of the video signal is lowered, the diaphragm drive circuit is controlled so that the amount of light emanating from the light source apparatus will be increased. This poses a problem that it becomes impossible to simultaneously control the source light so as to decrease the amount of source light.